Characterisation of the water expulsion vacuole in Phytophthora nicotianae zoospores
Date
1999-03
Authors
Mitchell, H J
Hardham, Adrienne R
Journal Title
Journal ISSN
Volume Title
Publisher
Springer Verlag
Abstract
The water expulsion vacuole (WEV) in zoospores of Phytophthora nicotianae and
other members of the Oomycetes is believed
to function in cell osmoregulation. We
have used videomicroscopy to analyse the
behaviour of the WEV during zoospore
development, motility and encystment
in P. nicotianae. After cleavage of
multinucleate sporangia, the WEV begins to
pulse slowly but soon attains a rate similar
to that seen in motile zoospores. In zoospores, the WEV has a mean cycle time
of 5.7 ± 0.71s. The WEV continues to pulse
at this rate until approximately 4 rain after
the onset of encystment. At this stage, pulsing slows progressively until it becomes
undetectable. The commencement of WEV operation in sporangia coincides with the
reduction of zoospore volume prior to release
from the sporangium. Disappearance of the
WEV during encystment occurs as formation
of a cell wall allows the generation of
turgot pressure in the cyst. As in other
organisms, the WEV in P. nicotianae zoospores
consists of a central bladder surrounded
by a vesicular and tubular spongiome.
Immunolabelling with a monoclonal antibody
directed towards vacuolar H⁺-ATPase
reveals that this enzyme is confined to
membranes of the spongiome and is absent
from the bladder membrane or zoospore plasma
membrane. An antibody directed towards plasma
membrane H⁺-ATPase shows the presence of this
ATPase in both the bladder membrane and the
plasma membrane over the cell body but not
the flagella. Analysis of ATPase activity
in microsomal fractions from P. nieotianae
zoospores has provided information on the
biochemical properties of the ATPases in
these cells and has shown that they are similar to those in true fungi. Inhibition
of the vacuolar H⁺-ATPase by potassium
nitrate causes a reduction in the pulse
rate of the WEV in zoospores and leads
to premature encystment. These results
give support to the idea that the vacuolar
H⁺-ATPase plays an important role in water
accumulation by the spongiome in oomycete
zoospores,as it does in other protists.
Description
Keywords
immunolabelling, Phytophthora nicotianae, plasma, membrane, H⁺-ATPase, water, expulsion, vacuole, zoospores
Citation
Collections
Source
Protoplasma 206.1-3 (1999): 118-130
Type
Journal article